The ambulance was just arriving for a worker who the window on the second floor fell o

问题补充：

The ambulance was just arriving, for a worker, who the window on the second floor, fell off the window.

A. had been repairing

B. was repairing

C. has been repairing

D. would be repairing

答案：

(答案→)A. had been repairing

B. was repairing

C. has been repairing

D. would be repairing

解析：考查时态。根据句意可知，工人修理窗户发生在掉落下来之前，即过去的过去，过去完成时